This paper analyzes the relative contributions of general reading comprehension and domain knowledge to subject matter text learning. The paper points out the limits of each factor in explaining text learning and summarizes some recent studies that support the complementary role played by each factor. A two-factor account of text learning (general ability and specific knowledge) is shown to be better but still inadequate without careful attention to the role of text structure, which includes both domain and strictly linguistic components. The paper concludes that these text components play pivotal but complex roles in text learning. (Twelve footnotes are included; 36 references are attached.) (Author/RS)